Consolidated fiber product



Patented Sept. 17, 1940 I UNITED STATES CONSOLIDATED FIBER rnonUc'rJoseph W. Gill, Elmhurst, Ill., assignor to'United States GypsumCompany, Chicago, 111., a corporation of Illinois No Drawing.Application July 3, 1935, Serial No. 29,735

3 Claims.

The present invention relates to a pressed board product and the processof its manufacture.

The primary object of the invention is the production of a hard, dense,coherent article of synthetic lumber,. usually in the form of boards orslabs which may be used for building purposes, interior decoration,panel boards, and the like.

One of the objects of the invention is the production of a boardcomposed substantially of cellulosic fibers or cellulosic and ligneousfibers in admixture with each other together with a comparatively smallamount of a binder such as vegetable or animal fatty-acid pitch,preferably with a sizing material, in conjunction with auxiliary bindersformed as a result of partial pyrolytic decomposition of the cellulosicor ligneous fibers. I

A further object of the invention is to produce synthetic lumber by aprocess which involves the fibration of a ligneous substance such aswood, or various plants, either by a mechanical or a chemical process,preferably the former,

followed by the reassembly of the resulting fibers into a.coherent mator slab after the incorporation with the fibers of a relatively smallamount of a vegetable or animal fatty-acid pitch. After theincorporation of these materials, the board may be subjected to heat andpressure within definite ranges, as will be more completely enumeratedhereinbelow,-whereby it will be consolidated into a hard, dense,coherent, water-resistant product.

The present process involves the formation from the ligneous andcellulosic material of autogenously-formed binders resulting from thepyrolytic decomposition of the li'gneous material and its associatedcellulosic complexes. The decomposition products then probably combinewith each other by condensation and polymerization, with the formationof resin-like binders which supplement the natural binders contained inthe material. The presence of the fatty-acid pitch further acts to bind.the material closely together while at the same time endowing it withproperties of toughness, resilience, and high water resistance.

The fatty-acid pitch preferably employed may be a by-product of themanufacture of soap. Thus when fats or oils are saponified orhydrolytically split so as to produce glycerol, fatty acids form oneproduct and glycerol the other.

The fatty acids are then distilled, usually under a vacuum. The darkresidue remaining" in the 55 still-used for this purpose constitutes thepitch,

which is capable of hardening when subjected to elevated temperatures,particularly in the presenceof oxygen.

The size used upon the fibers may consist of the ordinary rosin sizeused in the form of a 6 rosin soap, or may be a resin which is capableof saponi fication or emulsiflcation, although it is understood thatother waterproofing materials in the nature of waxes such as parafiinwax, carnauba wax, cer'esin wax, ozocerite wax, montan to wax, and thelike, may be used.

Broadly speaking, the present process comprises the fibration ofligneous material, although .this does not exclude the use of fiberswhich have been chemically liberated from wood. 15 Wood that has beenmerely mechanically fibrated forms the preferred embodiment of theinvention. Assuming that the manufacture is to proceed on the basis ofthe use of ground wood, which is usually ground in the presence of water20 by means of the usual pulp stones, the resulting pulp suspension isrun into a suitable tank provided with an agitator, and while therein istreated with a sizing material such, for example, as rosin size in anamount approximately 1% to .25 2% of the weight of the fibers. Thereisalso run into the tank up to 10% of a vegetable or animal fatty-acidpitch as, for example, stearin pitch, cotton-seed oil fatty-acid pitch,corn oil fattyacid pitch, or the like. Due to its viscosity and 30immiscibility in water it is preferable to add the pitch in the form ofan emulsion so that it'will be uniformly dispersed among the fibers. Asolvent for the pitchis preferably added to the pitch to facilitate itsemulsification. After the pitch' 35 and fibers have been mixed in thesaid tank, a sufflcient quantity of a precipitant such as alum oraluminum sulfate is added to decompose the rosin soapsize, with theformation-in the usual manner-of an insoluble precipitate which de- 40posits itself upon the fibers. The pitch that has been added tothemixture also is deposited on a the fibers. The resultant suspensionof treated fibers is now transferred to a suitable boardforming machinesuch as a Fourdrinier or Oliver board former, or other. mechanicalequivalent device, upon which it is formed into a wet mat. This mat isthen slightly compacted by being passed between squeeze rollers, allinthe mannerwell known in this art, whereupon the resultant damp mats aretransferred to a drier wherein they are dried, with the removal of allor substantially all ofthe moisture therein contained. The pitch,by'reason of the temperature used on the drier (250-350 F.) becomessomewhat hardor waxes, these being incorporated preferably in eitherfinely divided or emulsified form, although their use in the form ofsaponification products or soaps is not to be excluded. The amount ofpitch used varies approximately between 1% and 10% and is in thepreferred embodiment. present in an amount approximating 5%.

Assuming for the purposes of the present description that a board havingtwo plane fiat surfaces is to be made, the board formed as hereinabovedescribed is first thoroughly relieved of all the therein-containedvaporizable matter or moisture, and the board is then placed betweenheated surfaces such, for example, as the platens of a hydraulic press,whereupon impacting pressure is applied to said boards of up to 3000pounds per square inch for a period of from one minute up to one hourwithin a temperature range of from 400 F. to atemperature short of thepoint of active development of carbon for the materials. The ignitionpoint of wood is about 527 F. As a result of the applied pressure thereis brought about a consolidation of the board while at the same time theheat tends to decompose the cellulosic and ligneous constituentsthereof, with the autogenous formation of resinous and tarrycondensation products which act as auxiliary binders and serve to bindthe fibers of the board together into a strong and coherent mass.

If the board mats have been stored for some time, they will then containhygroscopic moisture which the: have'picked up from the atmosphere.Boards containing such moisture can be pressed if there be interposedbetween at least one surface thereof andthe heated platens someforaminous material such as a screen, in order to permit the escape ofmoisture which is converted into steam the boards and the platensheat-conducting caul plates of oxidized metal, or sheets coated withenamel or a glass-like composition. In stating the temperatures used inthe present process, it is understood that these temperatures aremeasured at the surface of the metallic heat-conducting'bodies that arein contact with the boards. Of course, if the platens themselves are ofoxidized metal or are coated with enamel or other glasslike composition,such intermediate sheets may then be dispensed with. At any rate, thetemperatures mentioned are the temperatures in contact with the boardand not the temperatures of the amount of the above-mentioned pitchysubstances to form fibers having these substances adhering thereto. Thethustreated fibers are then stored, either hot or cold, to allow theadded materials to harden somewhat. Thereupon the fibers aremechanically made into a mat, as by blowing them with an air currentonto a foraminous surface while applying suction to the latter.- If thefibers have absorbed any moisture, the mat is preferably dried and thenlaid onto the platens or the oxidized or enameled caul plates, andpressed in the manner already described.

The pressing time depends, of course, upon the temperature and thepressure used. It may be stated, as a general rule, that as thetemperature increases the time may safely be decreased, so that near theupper end of the temperature range stated the pressing time may be amatter of but a few minutes, while at the lower end it may extend verymuch longer.

,A somewhat similar effect is noticed in the case of pressures, and as ageneral rule the higher the pressure the shorter may be the pressingtime, although it is not to be understood that the relationship of thepressure to the time is the same as that of the temperature tothe time.

One of the advantages in interposing an oxidized metal caul plate or anenameled or glasslined caul plate between the boards being pressed andthe platens isthat such plates require little or no greasing or oiling,as they are naturally endowed with a tendency to obviate the sticking ofthe boards. This greatly simplifies manipulation and greatly facilitatesrapid and economical manufacturing operations.

In carrying the present invention into commercial practice, it has beenfound that there are distinct advantages in applying the impactingpressures in distinct stages or intervals, the pressure being either thesame at each period or different in each of the periods, as willpresently be explained. In any event, there is preferably a release ofpressure between the individual impactions. For example, mats havingpitch incorporated therein, completely relieved of their moisture, areplaced on caul plates and the assembly inserted between the platens of ahydraulic press. The temperature as measured at the surface of theseplatens may be, for example, between 445 F. and 455 F. The press is thenpreferably operated so as to bring the platens into contact with theboards, but without the application of any substantial pressure, for thepurpose of heating the surface of the boards to about the temperature ofthe platens. This usually takes from 1 to 3 minutes, although it may bevaried considerably. During this time, which can conveniently be' termedthe toasting period, the board surface will have acquired a temperaturesuificiently high so as to prevent the adhesion of the boards to thecaul plates. Although it is preferable to employ the toasting step,particularly when the temperature employed is in the upper portion ofthe range, the process may be carried out under certain conditionswithout the use of this toasting. However, even if the toasting is notabsolutely necessary, no harm can result from its use.

After the platens have been brought into contact with the boards forthis toasting step, or urged thereagainst under considerable pressurefor a short period of time, the pressure is released and the platens arepreferably separated from the surfaces of the boards. This separationmay be merely momentary or may extend for a few minutes. It has beenfound that in certain cases the ultimate strength of the boards for thepurpose of permitting the escapeof the accumulated gases and vapors. Abluish acrid smokewill generally be seen to rise from the boards andpass out between the platens,

The pressure may then be applied for a further period of abouttwo tothree minutes, whereupon it is again released in the same manner asalready described. At the more elevated temperatures it will be foundthat the pressing of the board is now completed, while, with temperatures around 450 F. and below, it may be desirable to again applypressure for another period of about two or three minutes, after whichthe pressure is released and the press opened.

Thereupon the boards are quickly removed from the press and immediatelysubjected 'to, a strong blast of air, preferably but not necessarilyheated, to remove as much as possible of the smoke and gases from thefreshly formed boards. This is done in order to remove the somewhatacrid' odor which would otherwise characterize the boards. The boardsmay then be passed through a passageway in which they are -subjected toa blast or current of cool air in order to relieve them of heat andallow them to become adjusted to normal atmospheric conditions withoutwarping.

The boards may also, if desired, be placed in a suitable oven in whichthey are subjected to a baking operation at about 300 F. for a period offrom two to six hours. This is particularly advantageous when the boardshave been stored before pressing for only a relatively short time, sothat the pre-oxidation of the pitch has not proceeded to the same extentas when they have been stored; The baking further modifies the pitch soas to increase its resistance to solvent. The strength of .the boards isalso enhanced by the baking.

As previously pointed out,'the time of pressing may generally beshortene as the temperature is increased. On the other hand, as thethickness of the board increases the time of pressing is preferablyextended. Thus, in forming board at a temperature of 445 to 455 F., thetotal pressing time, including the toasting, may be about 7 or 8minutes. This, however, may be shortened or lengthened according towhether the pressure employed is comparatively high or is in the lowerrange. As the thickness of the board increases, the time may beincreased so tain instances remain constant or decreased. The importantfeature, however, is to. release the pressureon the board at intervalsduring the pressing. In fact, a fairly high pressure may be applied, andafterthe. same is released the board may be treated, as during thetoasting step, with a very slight application of pressure, andthereafter, after total release of pressure, a high 2,215,246 boardpressure may be applied again. All of this obviously is subject toconsiderable variations, the

particular examples being given illustration only.

The boards produced by the present process for purposes of have a highmodulus of rupture, have low water absorption and a pleasing and smooth,polished surface. The fibers therein are consolidated together andcoalesced by the production of ai1-. togenously-produced resins andtarry condensation products which result from the heating of thetherein-contained cellulosio complexes, lig-v nins, and the like. Theinherent bonding powers of these autogenously-produced binders arefurther enhanced by the simultaneous presence of the pitches, which tendto plasticize and toughen the autogenously-produced binders. It will benoted that the amount of rosin size and pitches is relativelysmall,andunless the tem- "formed. binders with the fatty-acid pitches and sizewhich mutually contribute to the high degree of water resistance, lackof water absorption and final strength of the products made inaccordance with the present invention.

Applicant is aware of the fact that .waxes, oils and sizes have beenused in the past for the purpose of enhancing the water resistance offibrous products, but he is not aware that the autogenous development ofresins and condensation products conjointly with the use of fattyacidpitches or resins has ever been used before, and he considers this as adistinctstep in advance and as forming one of the essential elements ofhis present invention.

In the above formula the fatty-acid pitch is stantially ,infusible whensubjected to temperatures of from 259 to 300 F.

The fatty-acid pitches may be of any desired origin, such as cottonstearin pitch,cottonseed fatty-acid pitch, stearin pitch, orcottonsedoil foots pitch. All of these are now available as commercialproducts at a low cost, and for this reason the cost of carrying out thepresent invention is very low, so that it presents great commercialadvantages.-

.The products obtained are a pleasing lightbrown to chocolate-browncolor, and, because of their high modulus of rupture, lend themselves tomany industrial uses. Thus, they may be employed as table tops, wallpanels, packing cases, backing for signs, partitioning, paneling, andfor-general cabinet work. Due to their high water resistance; they mayalso be employed in certain types of outside work.

In carrying out this invention as previously described, various types offibers may be used, such as wood, cane, and vegetable, and the termlignocellulosic fibers, as used in the claims, is

intended to cover such fibers.

I claim: r 1. The process of producing a consolidated fiber productwhich comprises precipitating a fatty-acid pitch onto wood fiber whilein suspension in a liquid containing a fatty-acid pitch emulsion,forming the fiber into a coherent but relatively loose mat, allowingthe'pitch to become oxidized by access all air at ordinary-at-"mospheric temperature, compressing the resulting product at apressurenot exceeding about 3000 pounds per square inch and atemperature of at least 400 F., but one short of the point of.

the development of carbon and then subjecting the same to an oxidizingbake at about 300'1".'

{or a time'suflicient' to further harden the pitch.

2. The process of producing a consolidated fiber product which comprisesprecipitating a fatty-acid pitch onto wood fiber while in suspension ina liquid containing a fatty-acid pitch emulsion, forming the fiber intoa coherent but relatively loose mat, compressing the. mat at a':pressure not exceeding about 3000 pounds per amus square inch and atemperature of at least 400' F., but one short of the-point oi thedevelopment oi carbon, and then subjecting the same to an oxidizing bakeat about 300 F. for a time sulficientto harden the pitch.

-- 3'. The process oi producing a consolidated fiber product whichcomprises precipitating a and then subjecting the same to an oxidizingbake'at about 300 F. for a time sufllcient to further harden the pitch.

JOSEPH W. GILL.

